A material processing system must often precisely control position and velocity of objects moving through the system. Commonly, material processing systems control object movement by physically engaging the object with a separate object drive mechanism that moves the object at a predetermined velocity along a predetermined path. For example, gear driven ratchets, rollers, hooks, or conveyors are widely employed to move objects as diverse as paper, semiconductors, plastics, or steel by mechanically engaging the objects, and moving the engaged objects along a desired path at a fixed velocity. While commonplace, mechanical or frictional engagement of objects does have a disadvantage of requiring direct physical contact with an object. For certain applications, including processing of high purity or delicate materials, contamination or damage to the object may result from mechanical grasping or contact. This is particularly true for high speed processing systems, which may damage objects simply by engaging them. For example, high speed rollers may damage paper through differential engagement of misaligned paper with the roller, resulting in ripping or tearing of the paper.
Fortunately, mechanical or frictional engagement is only one possible means for moving an object. Object drive mechanisms based on various fluid support techniques have long been employed to move delicate objects without requiring solid mechanical contact. For example, instead of using conventional belts, conveyors or rollers, paper moving through xerographic copier systems can be supported on a laminar air flow, or uplifted and moved by directed air jets. This form of fluid support is particularly advantageous, for example, when sheets of paper carrying unfixed toner images must be moved between a photoconductive dram and a fusing station where the toner image is fixed. With conventional physical rollers, the continuing possibility of dynamic distortions to the toner image, or even slight misalignments resulting in image degradation, must always be considered. Problems with image degradation are particularly acute with color images, which must register multiple overlays created by separate color toner/fuser processing cycles to create the color image.
However, previous attempts to use fluid transport in high speed material processing systems that require accurate positioning have not been very effective. The disadvantages of commonly available fluid transport systems that use air jet mechanisms for support is most apparent when flexible objects such as continuous rolls of paper, sheets of paper, extruded plastics, metallic foils, wires, or optical fibers are transported. In such systems, the flexure modes can result in complex object behavior. Unlike rigid objects, flexible objects are dynamically unstable when supported by air jets, with edge curl, flutter, or other undesirable dynamic movements continuously occurring during support and transport. Such undesirable movements of the flexible object can result in mispositioning, transport failure, or even damaging surface contact between the flexible object and an air jet conveyor.
Accordingly, the present invention provides a fluid transport apparatus and method for moving a flexible object that does not require physical contact. The present invention can effectively work with either continuous or discrete flexible objects moving through a materials processing system. The present invention is a fluid transport system for moving a flexible object that includes a conveyor configured to direct fluid flow against opposite sides of the flexible object. A sensor unit is used to sense motion state of flexible object, where motion state is defined to include position, orientation, curvature, speed, or other desired positional or velocity information. A motion analysis unit is connected to the sensor unit to calculate trajectory of the flexible object during transport based on its sensed motion state. Trajectory calculations can include determination of overall object position, velocity, and orientation information, as well as position, velocity, and orientation of subregions within the object (such as caused by flexure). To ensure for dynamic adjustments necessary for transport of the flexible object, a motion control unit is connected to the motion analysis unit, with the motion control unit configured to modify fluid flow directed against opposite sides of the flexible object to adjust motion state of flexible objects. This permits correction of object misalignments, incorrect speed or travel path, or object pitch, roll, and yaw (if three dimensional orientation information is available), and even unwanted flutter, buckling, or edge curling.
In a most preferred embodiment of the present invention, paper or other graphically markable material is among the flexible objects capable of being tracked in accordance with the present invention. A paper handling system includes a plurality of opposed air jets adjusted for transport of paper, with at least a portion of the plurality of air jets being individually controllable. A sensing unit continuously (or intermittently) determines paper position, and an air jet control unit connected to the sensing unit is configured to modify paper trajectory in response to information received from the sensing unit. In response to the calculated position, the air jet control unit modifies paper movement or orientation (for example, by selectively increasing or decreasing air flow from air jets that impart momentum to defined subregions of the paper) to nearly instantaneously correct for discrepancies in the motion state of the paper, including its position, orientation, trajectory, velocity, flexure, or curvature. In preferred embodiments, the plurality of opposed air jets can be used to apply tensile or compressive forces to flatten paper, and the air jet control unit can be used to maintain paper in this flattened position during transport. Of course, other paper positions (in addition to flat) can also be maintained, with, for example, the plurality of opposed air jets being used to generate sufficient force to curve selected subregions of the paper.
Additional functions, objects, advantages, and features of the present invention will become apparent from consideration of the following description and drawings of preferred embodiments.